Monitoring camera

ABSTRACT

A monitoring camera is provided. The monitoring camera includes an image capturing unit configured to capture an image of a subject therein, the image capturing unit having an image capturing field angle adjustable by a zooming optical system; and a light source having a light emitting diode configured to emit an illuminating radiation. The camera further includes a lens unit configured to apply the illuminating radiation in a direction which is substantially identical to a direction in which the image capturing unit captures the image; and an irradiation moving unit configured to variably set an irradiation range of the illuminating radiation to irradiate an area which is substantially the same as the image capturing field angle of the image capturing unit.

CROSS REFERENCES TO RELATED APPLICATIONS

The present application claims priority to Japanese Patent ApplicationJP 2006-053285, filed in the Japanese Patent Office on Feb. 28, 2006,the entire contents of which being incorporated herein by reference.

BACKGROUND

The present application relates to a monitoring camera for applying aninfrared radiation, for example, to a subject to capture an image of thesubject.

In general, there have been provided monitoring cameras for capturingimages of suspicious objects or suspicious individuals for securityagainst crimes in shops, on streets, in parking lots, and in variousother places. Some monitoring cameras are combined with an infraredprojector for projecting an infrared radiation to a subject. Theinfrared projector is installed near the monitoring camera to apply theinfrared radiation to an image capturing range of the monitoring camera.The monitoring camera captures an image of the subject which isirradiated with the infrared radiation. Therefore, the monitoring cameracombined with the infrared projector is capable of monitoring a subjectand recording its image even at night or in a dark environment.

Monitoring cameras with a camera head swingable back and forth and upand down for an enlarged image capturing range are also in use. Such amonitoring camera may also be combined with a plurality of infraredprojectors to cover the swinging angle of the camera head for capturingimages in a wide image capturing range. Monitoring cameras incorporatinga small-size infrared projector have also been provided.

Japanese Patent Laid-open No. 2004-220147 discloses a monitoring cameraequipped with an illuminating infrared source.

The traditional monitoring camera with the projector cannot be remotelycontrolled to adjust its irradiation angle. Therefore, the projectoritself needs to have a sufficiently large irradiation range. If theprojector is to maintain a radiation flux density required for themonitoring camera to capture a desired image, then the projector isrequired to have a large output level. However, in order for theprojector to have a large output level, the projector has to be large insize. However, it is difficult to have a large-size projector mounted ona monitoring camera having a motor-driven swingable camera head which issubject to size limitations.

If a monitoring camera is combined with a small-size projector mountedon a camera head thereof, then the projector is capable of providingsufficient illuminance only within a short distance because theprojector itself is small in size. When a monitoring camera has its zoomlens shifted toward a telephoto end for capturing an image of a subjectin a far position, the amount of a radiation applied to the subjecttends to be insufficient if the projector has a fixed projection angle.Therefore, the infrared radiation application capability of theprojector limits the image capturing range of the monitoring camera.

SUMMARY

It is desirable to provide a monitoring camera which is capable ofappropriately applying a radiation to a subject to capture an image ofthe subject.

According to an embodiment, there is provided a monitoring cameraincluding an image capturing unit for capturing an image of a subjecttherein, the image capturing unit having an image capturing field angleadjustable by a zooming optical system, a light source having a lightemitting diode for emitting an illuminating radiation, a lens unit forapplying the illuminating radiation in a direction which issubstantially identical to a direction in which the image capturing unitcaptures the image, and an irradiation moving unit for variably settingan irradiation range of the illuminating radiation to irradiate an areawhich is substantially the same as the image capturing field angle ofthe image capturing unit.

With the above arrangement, the irradiation range of the illuminatingradiation can be varied to irradiate the area which is substantially thesame as the image capturing field angle of the image capturing unit, andthe image of the subject can be captured in the varied irradiationrange.

According to another embodiment, there is also provided a monitoringcamera including an image capturing unit for capturing an image of asubject therein through an optical system, a light source having aplurality of light emitting diodes for emitting an illuminatingradiation, and a controller for controlling energization patterns of thelight emitting diodes in synchronism with an image capturing timinginterval of the image capturing unit.

With the above arrangement, energization patterns of the light emittingdiodes can be controlled in synchronism with the image capturing timinginterval of the image capturing unit, and the image of the subject canbe captured while the subject is being irradiated with the radiationemitted according to the controlled energization patterns.

Since the irradiation range of the illuminating radiation can be variedto irradiate the area which is substantially the same as the imagecapturing field angle of the image capturing unit, and the image of thesubject can be captured in the varied irradiation range, it is possibleto apply an appropriate amount of radiation to illuminate the subject tocapture the image thereof.

Furthermore, because energization patterns of the light emitting diodescan be controlled in synchronism with the image capturing timinginterval of the image capturing unit, and the image of the subject canbe captured while the subject is being irradiated with the radiationemitted according to the controlled energization patterns, the lightemitting diodes do not need to be energized at all times, and hence mayconsume a reduced amount of electric power.

Additional features and advantages are described herein, and will beapparent from, the following Detailed Description and the figures.

BRIEF DESCRIPTION OF THE FIGURES

FIG. 1 is a view showing an example in which a monitoring cameraaccording to an embodiment is installed;

FIG. 2 is a block diagram of internal structures of the monitoringcamera according to an embodiment and a central controller;

FIG. 3 is a cross-sectional view showing an example of the monitoringcamera according to an embodiment;

FIGS. 4A and 4B are views showing how infrared radiation applicationranges and image capturing field angles of the monitoring cameraaccording to an embodiment are ganged;

FIG. 5 is a cross-sectional view showing another example of themonitoring camera according to an embodiment;

FIGS. 6A and 6B are views showing examples of different light sourceenergization patterns for achieving different irradiated states with amonitoring camera according to a second embodiment;

FIG. 7 is a graph showing an example of intermittent irradiation only invalid frames according to the second embodiment;

FIG. 8 is a diagram showing an example of an irradiated area required tocapture an image according to the second embodiment;

FIG. 9 is a cross-sectional view showing an example of a monitoringcamera according to a third embodiment, which employs optical fibers toincrease the freedom with which to position a light source;

FIG. 10 is a cross-sectional view showing another example of themonitoring camera according to the third embodiment, which employsreflecting mirrors to collect light for the optical fibers;

FIG. 11 is a cross-sectional view showing still another example of themonitoring camera according to the third embodiment, which employs amultireflector and a lens array to collect light for the optical fibers;

FIG. 12 is a cross-sectional view showing yet another example of themonitoring camera according to the third embodiment, which employs acondensing light source; and

FIGS. 13A, 13B, and 13C are perspective views of monitoring camerasaccording to other embodiments.

DETAILED DESCRIPTION

A monitoring camera according to a first embodiment will be describedbelow with reference to FIGS. 1 through 5. According to the firstembodiment, the principles of the invention are applied to a monitoringcamera with a zooming function which incorporates therein a light sourcefor applying an infrared radiation to a subject to capture an image ofthe subject even at night.

External structural details of the monitoring camera according to thefirst embodiment will first be described below with reference to FIG. 1.FIG. 1 shows an example in which the monitoring camera according to thefirst embodiment is installed. In the illustrated example, themonitoring camera, denoted by 100, is substantially in the form of arectangular parallelepiped and applies an infrared radiation to asubject to capture an image of the subject even at night. The monitoringcamera 100 is mounted on an outer wall of a building. The monitoringcamera 100 incorporates therein a light source including a plurality oflight-emitting diodes (LEDs) for emitting an infrared radiation. Themonitoring camera 100 also has a Fresnel lens 14, which is a planarlens, for emitting an infrared radiation from the light source out ofthe monitoring camera 100. The Fresnel lens 14 applies illuminatinglight (infrared radiation) from the monitoring camera 100 in a rangewhich is substantially the same as the image capturing field angle 51 ofthe monitoring camera 100. The infrared radiation emitted from the lightsource passes through the Fresnel lens 14 and is applied in anirradiation range 50 to irradiate a subject 55. The Fresnel lens 14 hasa central through hole 14 a in which a camera lens 1 for capturing asubject image is disposed. The camera lens 1 includes a zoom lens with avariable image capturing field angle. Therefore, the monitoring camera100 has a zooming function. The irradiation range 50 of the illuminatinglight irradiates an area which is substantially the same as the imagecapturing field angle 51 in which the camera lens 1 of the monitoringcamera 100 captures an image.

An image captured by the monitoring camera 100 is transmitted to acentral controller 30 which controls operation of the monitoring camera100 and is recorded in the central controller 30. The central controller30 has a video output terminal connected to a display monitor 40 fordisplaying images. The central controller 30 displays a captured imagetransmitted directly from the monitoring camera 100 on the displaymonitor 40 in real time, or displays recorded image data read from ahard disk drive in the central controller 30 on the display monitor 40.The central controller 30 may also display captured images supplied froma plurality of monitoring cameras 100 installed in different places, asa segmented image screen on the display monitor 40. The centralcontroller 30 generates a control signal based on a user's action on aconsole panel 33 having various switches or an automatic timer setting,and transmits the generated control signal to the monitoring camera 100.Using the control signal, the central controller 30 can vary the imagecapturing field angle and the irradiation range 50 of the illuminatinglight based on the zooming function of the monitoring camera 100.

Internal structural details of the monitoring camera 100 and the centralcontroller 30 will be described below with reference to FIG. 2. Themonitoring camera 100 captures an image in an image capturing rangethrough the camera lens 1, which includes optical components such as aplurality of zoom lenses. Incident light applied to the camera lens 1travels through an iris 2 for aperture control and is focused onto animage capturing surface of a CCD (Charge Coupled Device) image capturingdevice 4. The iris 2 controls the size of an aperture for passing theincident light therethrough based on a control signal generated by agenerator 10 which control various parts of the monitoring camera 100.The CCD image capturing device 4 outputs an image signal depending on asubject image focused on the image capturing surface thereof.

The image signal output from the CCD image capturing device 4 is appliedto an analog signal processor 5 which performs analog signal processingon the image signal. Specifically, the analog signal processor 5performs a sampling/holding process and an automatic gain controlling(AGC) process on the image signal, and outputs a processed analog imagesignal. The analog image signal is applied to an analog-to-digital (A/D)converter 6, which coverts the analog image signal into a digital imagesignal by sampling the analog image signal at a predetermined samplingrate. The digital image signal is then output from the A/D converter 6to a digital signal processor 7 which performs digital signal processingon the digital image signal. Specifically, the digital signal processor7 generates various signals required for framing, still image capturing,etc. from the digital image signal through such digital signalprocessing. The camera lens 1, the iris 2, the CCD image capturingdevice 4, the analog signal processor 5, A/D converter 6, and thedigital signal processor 7 will also be collectively referred to as acamera block 17. The monitoring camera 100 has an infrared cutofffilter, not shown, that can selectively be positioned in and out of theoptical path leading to the CCD image capturing device 4. For daytimemonitoring, the infrared cutoff filter is placed in the optical path forthe CCD image capturing device 4 to capture an image based on visiblelight. For nighttime monitoring, the infrared cutoff filter is placedout of the optical path for the CCD image capturing device 4 to capturean image based on an infrared radiation.

Various processing and operational sequences of the monitoring camera100 are controlled by the controller 10. The controller 10 readsprocessing programs, parameters, and data used for controlling thevarious parts from a writable memory 11 on an as-needed basis, performsvarious processing processes, and stores required parameter and datainto the memory 11. The controller 10 also controls an emission driver16 to energize a light source 15 to emit an infrared radiation.

The monitoring camera 100 incorporates therein the light source 15 foremitting an infrared radiation. The light source 15 includes alight-emitting diode array of a plurality of light-emitting diodesmounted on a board 20 (see FIG. 3) integrally combined with racks 18. Aninfrared radiation emitted from the light source 15 on the racks 18 istransmitted as an illuminating radiation through the Fresnel lens 14which has an optical axis substantially in the direction along which thecamera block 17 captures images. The racks 18 are held in mesh withgears operationally connected to motors 13. When the motors 13 areenergized, the gears are rotated to cause the racks 18 to move the board20 along the optical axis of the camera lens 1 to vary the irradiationrange of the illuminating radiation. By thus varying the irradiationrange of the illuminating radiation, the light source 15 is moved toirradiate an area which is substantially the same as the image capturingfield angle of the camera block 17.

The central controller 30 has a controller 32 for controlling variousparts of the central controller 30. Based on a user's action on theconsole panel 33 (see also FIG. 1), the controller 32 reads processingprograms, parameters, and data used for controlling the various partsfrom a writable memory 36, and performs various processing processes.The central controller 30 has a communication interface 31 which can beconnected to a communication interface 9 of the monitoring camera 100for transmitting data to and receiving data from the monitoring camera100. When the communication interfaces 9, 31 are connected, the centralcontroller 30 transmits a control signal generated thereby through thecommunication interface 31 to the monitoring camera 100 for remotelycontrolling the monitoring camera 100 to perform zooming operation ofthe camera block 17 and adjusting the irradiation range of theilluminating radiation. The central controller 30 also receives capturedimages from the monitoring camera 100 through the communicationinterface 31.

The controller 32 adds an image capturing time to a received capturedimage based on time information that is read from a clock unit 37 havinga timing function, and records the captured image with the added imagecapturing time in a hard disk drive 35 which serves as a mass storagerecording medium. The controller 32 can also read times from the clockunit 37 and start and end capturing an image with the monitoring camera100 at preset image capturing start and end times. The controller 32records captured images in the hard disk drive 35 at successive imagecapturing times. The central controller 30 has an image output unit 34for supplying captured images read from the hard disk drive 35 to thedisplay monitor 40. The controller 32 controls the image output unit 34to output captured images to display monitor 40 to display the capturedimages thereon.

Internal structural details of the monitoring camera 100 will further bedescribed below with reference to FIG. 3. FIG. 3 shows the monitoringcamera 100 in cross section. As shown in FIG. 3, linear guides 19 aremounted on inner wall surfaces of the housing of the monitoring camera100 along the optical axis of the camera lens 1. The racks 18 arelinearly movable on and along the linear guides 19 by a powertransmitting mechanism of gears, etc. which can be actuated when themotors 13 are energized. According to the present embodiment, the lightsource 15 has a plurality of infrared emitting diodes 21 mounted on theboard 20 which extends substantially parallel to the Fresnel lens 14.The board 20 with the infrared emitting diodes 21 mounted thereon ismovable toward and away from the Fresnel lens 14 in response toenergization of the motors 13. When the board 20 is thus moved, theimage capturing field angle of the monitoring camera 100 varies in arange from 3° to 60° in the forward direction of the monitoring camera100. Each of the infrared emitting diodes 21 has an irradiation angleranging from 20° to 30°, for example. The irradiation range of theilluminating radiation is variable such that the infrared radiationemitted from the infrared emitting diodes 21 irradiates an area which issubstantially the same as the image capturing field angle of the camerablock 17 by passing through the Fresnel lens 14. The racks 18 aremovable along the linear guides 19 by the motors 13 depending on thezoom ratio of the camera block 17. The irradiation range of theilluminating radiation is variable based on the positional relationshipbetween the Fresnel lens 14 and the light source 15.

Ganged operational relationship between infrared radiation applicationranges and image capturing field angles of the monitoring camera 100will be described below with reference to FIGS. 4A and 4B. Themonitoring camera 100 with the zooming function can selectively be setto a wide-angle mode and a telephoto mode. FIG. 4A shows an example ofan infrared radiation application range and an image capturing fieldangle in the wide-angle mode, and FIG. 4B shows an example of aninfrared radiation application range and an image capturing field anglein the telephoto mode. The irradiation range 50 of the monitoring camera100 is selected to irradiate an area which is slightly greater than theimage capturing field angle 51. However, since the irradiation angle ofthe infrared radiation is governed by the distribution characteristicsof the applied illuminating radiation, the irradiation range 50 may belarge enough to recognize the subject 55 when its image is to becaptured even if the irradiation range 50 falls within the imagecapturing field angle 51.

If the image capturing field angle 51 is spread as shown in FIG. 4A,then the light source 15 is displaced toward the Fresnel lens 14 towiden the irradiation range 50 of the illuminating radiation. On theother hand, if the image capturing field angle 51 is narrowed as shownin FIG. 4B, then the light source 15 is displaced away from the Fresnellens 14 to narrow the irradiation range 50 of the illuminatingradiation. Therefore, the irradiation range 50 of the illuminatingradiation is variable in ganged relation to the zooming action of thecamera lens 1 to change the image capturing field angle 51.

Accordingly, it is possible to vary the irradiation range 50 of theilluminating radiation so as to irradiate an area which is substantiallythe same as the image capturing field angle 51 of the monitoring camera100, for capturing an image of the subject 55.

According to the present embodiment, the monitoring camera 100 iscapable of varying the irradiation range 50 of the illuminatingradiation substantially in the same manner as with the image capturingfield angle 51 which varies as the camera block 17 makes a zoomingaction between the telephoto mode and the wide-angle mode. As a result,the monitoring camera 100 can apply an appropriate amount of infraredradiation depending on the position and size of the subject 55 to beimaged. The monitoring camera 100 can reliably capture an image of thesubject 55 without an illuminating radiation shortage even when thesubject 55 is located far away from the monitoring camera 100.

In the first embodiment described above, an infrared radiation isemitted from the infrared emitting diodes 21 mounted on the planar board20. However, as shown in FIG. 5, an infrared radiation may be emittedfrom a plurality of infrared emitting diodes 21 mounted on a curvedboard 20′ which is convex outwardly, i.e., toward the Fresnel lens 14.Details of the monitoring camera shown in FIG. 5, other than the curvedboard 20′, are identical to those of the monitoring camera 100 shown inFIG. 3. Since the light source has its radiation distributioncharacteristics changed by changing the layout of the infrared emittingdiodes, the distribution characteristics of the applied illuminatingradiation can be changed for a wider irradiation range.

A monitoring camera 200 according to a second embodiment will bedescribed below with reference to FIGS. 6A, 6B, 7, and 8. The monitoringcamera 200 is capable of varying the irradiation range of theilluminating radiation by changing light source energization patterns.

First, internal structural details of the monitoring camera 200 will bedescribed below. The monitoring camera 200 has a light source 24 foremitting an infrared radiation, the light source 24 including a total ofnine infrared emitting diodes 21 a through 21 i arranged in threevertical columns and three horizontal rows and mounted on the board 20.The monitoring camera 200 also has a microlens array 22 disposed infront of the board 20 for converting infrared radiations emitted fromthe respective infrared emitting diodes 21 a through 21 i into aparallel beam, and a projector optical system lens 23 disposed in frontof the microlens array 22 for enlarging the irradiation range of theilluminating radiation from the microlens array 22. The monitoringcamera 200 has a signal processing system which is identical to thesignal processing system of the monitoring camera 100 according to thefirst embodiment shown in FIG. 2. The monitoring camera 200 differs fromthe monitoring camera 100 in that the controller 10 controls lightsource energization patterns peculiar to the second embodiment.

Examples of light source energization patterns of the monitoring camera200 will be described below. When the monitoring camera 200 detects amoving subject 55, the monitoring camera 200 changes energizationpatterns of the light source 24 to follow the subject to apply theilluminating radiation to the subject or intermittently energizes thelight source 24 at given emission intervals to apply the illuminatingradiation to the subject. These functions of the monitoring camera 20are achieved under the control of the controller 10 which operatesaccording to control commands from the central controller 30. When themonitoring camera 200 detects a moving subject 55, the controller 10 canalso individually energize the infrared emitting diodes 21 a through 20i according to full or partial energization patterns read from thememory 11.

FIG. 6A shows a first light source energization pattern by way ofexample. According to the first light source energization pattern, adiagonal array of infrared emitting diodes on the board 20 areenergized. Specifically, when the monitoring camera 200 detects themoving subject 55 which moves diagonally as shown in FIG. 6A, thecontroller 10 energizes the infrared emitting diodes 21 a, 21 e, 21 iand de-energizes the other infrared emitting diodes. Infrared radiationsemitted from the infrared emitting diodes 21 a, 21 e, 21 i pass throughthe microlens array 22 and the optical system lens 23, and illuminateirradiated areas 53 a, 53 e, 53 i on a diagonal line of a captured image52.

FIG. 6B shows a second light source energization pattern by way ofexample. According to the second light source energization pattern, alower array of infrared emitting diodes on the board 20 are energized.Specifically, when the monitoring camera 200 detects the moving subject55 which moves horizontally, as shown in FIG. 6B, the controller 10energizes the infrared emitting diodes 21 g, 21 h, 21 i and de-energizesthe other infrared emitting diodes for following the subject 55.Infrared radiations emitted from the infrared emitting diodes 21 g, 21h, 21 i pass through the microlens array 22 and the optical system lens23, and illuminate irradiated areas 53 g, 53 h, 53 i on a lowerhorizontal line of the captured image 52.

In FIGS. 6A and 6B, three infrared emitting diodes are simultaneouslyenergized. However, only one or two infrared emitting diodes may besimultaneously energized.

In the second embodiment shown in FIGS. 6A and 6B, the light sourceenergization patterns are controlled. These light source energizationpatterns may be combined with an intermittent light source energizationpattern to be described below for more efficient generation ofilluminating radiation. An example of intermittent infrared irradiationonly in valid frames according to the second embodiment will bedescribed below with reference to FIG. 7. FIG. 7 shows a graph having ahorizontal axis representing time and a vertical axis the level ofemitted infrared radiation. In this example, the monitoring camera 200has its infrared emitting diodes not continuously energized, butintermittently energized in synchronism with an image capturing timinginterval of the camera block 17.

A traditional monitoring camera has its infrared emitting diodescontinuously energized for monitoring. In FIG. 7, the traditionalmonitoring camera emits a level L2 of infrared radiation continuouslyfor times t1 through t4 from the infrared emitting diodes. Themonitoring camera 200 according to the present embodiment shown in FIG.7 has its infrared emitting diodes energized for strobe emission for astrobe emission period T=t4−t1 in synchronism with an image capturingtiming interval. An image capturing timing interval from time t2 to timet3 represents a valid frame, and a timing interval from time t3 to timet5 represents an invalid frame. Time t5−t4 is equal to time t2−t1. Themonitoring camera 200 emits a level L1 of infrared radiationintermittently for times t2 through t3 from the infrared emittingdiodes. If the amount of emission energy produced by the level L1 ofinfrared radiation for times t2 through t3 is equal to the amount ofemission energy produced by the level L2 of infrared radiation fromtimes t1 through t4, then the infrared emitting diodes can emit astronger level of infrared radiation in synchronism with the imagecapturing timing interval to give a far subject an amount of infraredradiation required to capture an image of the subject.

An example in which only an area required to capture an image isirradiated in synchronism with the image capturing timing interval willbe described below with reference to FIG. 8. FIG. 8 shows a diagramhaving a horizontal axis representing time with an array of capturedimages 52 arranged at respective times. The monitoring camera 200according to the present embodiment shown in FIG. 8 has its infraredemitting diodes energized for strobe emission in synchronism with animage capturing timing interval of the camera block 17, and also changesenergization patterns of the infrared emitting diodes in order to followa moving subject. Specifically, the monitoring camera 200 controls thelight source 24 to emit an infrared radiation at intervals T1 (in sec.)according to a pattern or to emit an infrared radiation at intervals T2(in sec.) according to another pattern wherein the intervals T1 arelonger than the intervals T2 (T1>T2). Similarly, the monitoring camera200 controls the camera block 17 to capture images at image capturingtiming intervals T1 (in sec.) or to capture images at image capturingtiming intervals T2 (in sec.) wherein the intervals T1 are longer thanthe intervals T2 (T1>T2). If there is no moving subject 55 detected incaptured images 52 output from the camera block 17, then the monitoringcamera 200 controls the light source 24 to emit an infrared radiation atthe intervals T1. The controller 10 selects a lower frame rate forincreased infrared radiation emission intervals, and applies theilluminating radiation to the entire image capturing range. If there isa moving subject 55 detected in captured images 52 output from thecamera block 17, then the monitoring camera 200 controls the lightsource 24 to emit an infrared radiation at the intervals T2 and alsocontrols the camera block 17 to capture images at image capturing timingintervals T2. The controller 10 selects a higher frame rate for reducedinfrared radiation emission intervals, and applies the illuminatingradiation to a portion, which includes the subject 55, of the entireimage capturing range to change light source energization patterns inorder to follow the moving subject 55. Each of the intervals T1 may be 1second, and each of the intervals T2 may be 1/30 second.

In this manner, the monitoring camera 200 is capable of capturing imagesby changing image capturing timing intervals and light sourceenergization patterns.

According to the second embodiment, when the light source is energizedintermittently, the electric power consumption is reduced and the amountof heat generated by the monitoring camera is also reduced. However, thelight source can apply an intensive illuminating radiation insynchronism with the image capturing timing intervals of the camerablock. As a result, the monitoring camera achieves a sufficient level ofilluminance at positions far the monitoring camera to make capturedimages highly bright, and can capture images positioned at greaterdistances from the monitoring camera at night. When a subject isdetected, the image capturing timing intervals are shortened to captureimages of the subject at a higher frame rate. Consequently, images ofthe subject can reliably be captured even if the subject moves quickly.Since the light source includes infrared emitting diodes, it can switchinstantaneously between the energized state and the de-energized state,allowing images of the subject to be captured depending on the motion ofthe subject.

When the image capturing range is monitored ordinarily with no subjectdetected, its image is captured at a lower frame rate. Even if the imagecapturing range is monitored for a long period of time, therefore, theamount of data of captured images to be recorded may be small.Accordingly, the required amount of data may be recorded in a recordingdevice such as a hard disk drive, a tape drive, or the like for anincreased period of time. If images are recorded in a tape drive, thenthe tape in the tape drive may be replaced less frequently.

In FIGS. 6A and 6B, a diagonal array of infrared emitting diodes and alow array of infrared emitting diodes, respectively, are energizedsimultaneously. However, the infrared emitting diodes to be energizedare not limited to the patterns shown in FIGS. 6A and 6B. If a pluralityof subjects 55 are detected at opposite ends of the image capturingrange 52, the emitted infrared radiation may be applied to the subjects55 only. In this manner, the electric power consumption of the lightsource is further reduced, and the freedom with which to switch betweenirradiation ranges is increased.

In FIGS. 6A and 6B, the light source includes a total of nine infraredemitting diodes 21 a through 21 i arranged in three vertical columns andthree horizontal rows. However, the number of infrared emitting diodesthat can be used is not limited to nine, but the light source mayinclude more or less infrared emitting diodes depending on thecircumstances in which the monitoring camera is used.

In FIG. 7, the amount of emission energy produced by the level L1 ofinfrared radiation for times t2 through t3 is equal to the amount ofemission energy produced by the level L2 of infrared radiation fromtimes t1 through t4. However, there is a situation where a high level ofinfrared radiation may not be required when the image capturing range ismonitored ordinarily with no subject detected. In such a situation, theinfrared radiation emission intervals may be increased to reduce theamount of emission energy produced by the level L1 of infrared radiationfor times t2 through t3, for thereby lowering the electric powerconsumption. If the monitoring camera is powered by a limited powersupply such as a battery or the like, then the increased infraredradiation emission intervals are effective to prolong the service lifeof the battery.

A monitoring camera 300 according to a third embodiment will bedescribed below with reference to FIGS. 9 through 12. The monitoringcamera 300 employs a light guide in the form of optical fibers toincrease the freedom with which to position a light source. Themonitoring camera 300 has a signal processing system which is identicalto the signal processing system of the monitoring camera 100 accordingto the first embodiment shown in FIG. 2. The monitoring camera 300differs from the monitoring camera 100 in that it has a light sourcepeculiar to the third embodiment.

First, internal structural details of the monitoring camera 300 will bedescribed below. FIG. 9 shows in cross section the monitoring camera 300which employs optical fibers 63 for guiding a infrared radiation frominfrared emitting diodes of a light source 25 to a Fresnel lens 14′.Specifically, the infrared radiation from the infrared emitting diodesof the light source 25 is collected by a reflector 64 having acircularly curved inner reflecting surface toward a first terminal end63 a of the optical fibers 63. The optical fibers 63 are capable oftransmitting the infrared radiation applied to the first terminal end 63a therethrough to a second terminal end 63 b, opposite to the firstterminal end 63 a, and emitting the transmitted infrared radiation fromthe second terminal end 63 b without any substantial loss. The infraredradiation applied to the first terminal end 63 a passes through theoptical fibers 63 and is emitted from the second terminal end 63 b. Theemitted infrared radiation is converted from a converged beam into aspread beam by a diffusion plate 62. The infrared radiation emitted fromthe diffusion plate 62 passes a zoom lens 61 and the Fresnel lens 14′,and is applied to the image capturing range of the monitoring camera300. Although the light source 15 according to the first embodiment ismovable, the light source 25 of the third embodiment is not movable, butthe zoom lens 61 is movable to enlarge or contract the infraredradiation beam emitted from the second terminal end 63 b of the opticalfibers 63 before the infrared radiation passes through the Fresnel lens14 and is applied as the illuminating radiation to the image capturingrange.

According to the third embodiment, the light source 25 of theilluminating radiation may be located at a position spaced from themonitoring camera 300.

For example, the optical fibers 63 allow the light source 25 to bespaced from the Fresnel lens 14′ of the monitoring camera 300.Therefore, as shown in FIG. 9, the light source 25 may be disposedbehind the camera block 17 in the housing of the monitoring camera 300.Therefore, the monitoring camera 300 itself may be reduced in size.Alternatively, the light source 25 may not be placed in the housing ofthe monitoring camera 300, but may be located outside of the housing ofthe monitoring camera 300 to transmit the infrared radiation through theoptical fibers 63 into the monitoring camera 300. The alternativearrangement makes it possible to further reduce the size of themonitoring camera 300.

In the third embodiment, the infrared radiation from the light source 25is collected by the reflector 64. However, the infrared radiation fromthe light source 25 may be guided to the optical fibers 63 by any ofvarious other structures. FIGS. 10 through 12 show such other structuresfor guiding or collecting the infrared radiation from the light sourcetoward the optical fibers 63.

FIG. 10 shows a structure in which the infrared radiation emitted fromthe light source is collected by two reflecting mirrors that confronteach other. The light source includes an infrared emitting diode chip26. The infrared radiation emitted from the infrared emitting diode chip26 is reflected by a concave reflecting mirror 66 and focused to aposition at the focal point of the reflecting mirror 66. The firstterminal end 63 a of the optical fibers 63 is disposed near the focalpoint of the reflecting mirror 66. Another smaller-diameter concavereflecting mirror 65 is positioned near the infrared emitting diode chip26 in confronting relation to the reflecting mirror 66 for directing theinfrared radiation emitted from the infrared emitting diode chip 26toward the reflecting mirror 66. With the arrangement shown in FIG. 10,the infrared radiation emitted from the infrared emitting diode chip 26is collected by the reflecting mirrors 65, 66 toward the first terminalend 63 a of the optical fibers 63. The collected infrared radiation istransmitted through the optical fibers 63 and then emitted from thesecond terminal end 63 b.

FIG. 11 shows a structure in which the infrared radiation emitted from alight source 27 is collected by a multireflector. Specifically, amicrolens array 67 for producing parallel beams is disposed in front ofa plurality of infrared emitting diodes of the light source 27. Theinfrared radiation emitted from the light source 27 is converted by themicrolens array 67 into parallel beams, which are reflected by a concavemultireflector 68 and focused onto the first terminal end 63 a of theoptical fibers 63. The infrared radiation beam applied to the firstterminal end 63 a travels through the optical fibers 63 and then isemitted from the second terminal end 63 b.

FIG. 12 shows a structure in which the infrared radiation emitted from aplurality of light sources. Specifically, concave reflectors 69 aredisposed respectively around light sources 28 and have respective focalpoints positioned at the first terminal end 63 a of the optical fibers63. The infrared radiation emitted from the light sources 28 arereflected by the respective reflectors 69 and focused onto the firstterminal end 63 a of the optical fibers 63. The infrared radiation beamapplied to the first terminal end 63 a travels through the opticalfibers 63 and then is emitted from the second terminal end 63 b.

In the third embodiment described above, the optical fibers 63 are usedas a light guide. However, any of various other members capable ofemitting a radiation applied to one end thereof from the other endthereof may be employed as a light guide.

According to the first through third embodiments described above, sincethe monitoring camera can employ various different light sources andemission patterns, a effective illuminating radiation can be applied toa subject positioned in the image capturing range to capture an image ofthe subject. Images of subjects, which have heretofore been difficult tocapture at night unless a combination of a large-size projector and alarge-size motor-driven camera platform are used, can be captured by asingle monitoring camera combined with a small-size light source.According to an embodiment, the monitoring camera can be installed in areduced installation space at a reduced installation cost. The imagecapturing field angle and the irradiation range of the monitoring cameracan freely be controlled in a ganged fashion. Inasmuch as the infraredradiation emitted from the light source can be efficiently guided to aposition near the camera block, the light source may be reduced in size.The light source in the form of light-emitting diodes is capable ofemitting a required amount of radiation even though it consumes a smallamount of electric power, and hence may be of a low electric powerrequirement.

In the first through third embodiments described above, the light sourceincludes infrared emitting diodes. However, the light source may includelight-emitting diodes for emitting visible light. Alternatively,infrared emitting diodes and light-emitting diodes may be combined witheach other and may alternatively be energize to selectively emit aninfrared radiation and visible light. White-light-emitting diodes areeasy and convenient to use because they are less liable to deteriorateeven when used over a long period of time and are highly durable wheninstantaneously energized. The light source for emitting visible lightmay include a halogen lamp, a fluorescent tube, or the like.

The arrangement for varying the irradiation angle depending on the imagecapturing field angle, the arrangement for changing light sourceenergization patterns to intermittently energize the light source, andthe arrangement for guiding the infrared radiation through the lightguide, as described above according to the first through thirdembodiments, may be combined in any of various possible combinations.

The recording device incorporated in the central controller 30 includesthe hard disk drive 35 in the illustrated embodiment. However, capturedimages may be recorded in any of various recording mediums including anoptical disk, a magnetic disk, a magneto-optical disk, a flash memory,at the like.

In the first through third embodiments described above, the light sourceand the camera block are accommodated in the monitoring camera housingin the form of a rectangular parallelepiped. However, the monitoringcamera may have a housing having another shape. FIGS. 13A through 13Cshow motor-driven swingable PTZ (Pan-Tilt-Zoom) monitoring camerashaving an infrared emitter for emitting an infrared radiation from alight source incorporated therein. Each of the motor-driven swingablePTZ monitoring cameras shown in FIGS. 13A through 13C includes adome-shaped camera having a camera block and a projector, and can berotated about vertical and horizontal axes (not shown).

Specifically, FIG. 13A shows a monitoring camera 400 having a cameralens and an infrared emitter whose respective axes are aligned with eachother. Specifically, the monitoring camera 400 is fixedly mounted on abase 71. The monitoring camera 400 includes a horizontally movable unit72 disposed on the base 71 for rotation through horizontal angles and avertically movable unit 73 disposed in the horizontally movable unit 72for rotation through vertical angles. The vertically movable unit 73houses therein an infrared emitter 75 having a Fresnel lens and a cameralens 1 coaxial with the infrared emitter 75.

FIG. 13B shows a monitoring camera 410 having a camera lens and aninfrared emitter whose respective axes are spaced from and extendparallel to each other. Specifically, the monitoring camera 410 isfixedly mounted on the base 71. The monitoring camera 410 includes thehorizontally movable unit 72 disposed on the base 71 and the verticallymovable unit 73 disposed in the horizontally movable unit 72. Thevertically movable unit 73 houses therein the infrared emitter 75 andthe camera lens 1 whose respective axes are spaced from and extendparallel to each other.

FIG. 13C shows a monitoring camera 420 having a camera lens and fourinfrared emitters, the infrared emitters having respective axes disposedaround the camera lens. Specifically, the monitoring camera 420 isfixedly mounted on the base 71. The monitoring camera 420 includes thehorizontally movable unit 72 disposed on the base 71 and the verticallymovable unit 73 disposed in the horizontally movable unit 72. Thevertically movable unit 73 houses therein the camera lens 1 and fourinfrared emitters 76 a through 76 d which are disposed around the cameralens 1. The infrared emitters 76 a through 76 d have respective axesparallel to the optical axis of the camera lens 1.

The monitoring cameras 400, 410, 420 may be electrically connected to acentral controller for setting swinging angles and swinging patterns tovary an image capturing range and adjust an irradiation angle dependingon a camera zooming action. The motor-driven swingable monitoringcameras with the projector incorporated in their head are thus capableof providing a sufficient distance over which the radiation is to beprojected and a sufficient level of illuminance over the distance, forthereby achieving an increased monitoring capability.

It should be understood that various changes and modifications to thepresently preferred embodiments described herein will be apparent tothose skilled in the art. Such changes and modifications can be madewithout departing from the spirit and scope of the present subjectmatter and without diminishing its intended advantages. It is thereforeintended that such changes and modifications be covered by the appendedclaims.

1. A monitoring camera comprising: an image capturing unit configured tocapture an image of a subject therein, said image capturing unit havingan image capturing field angle adjustable by a zooming optical system; alight source including a light emitting diode configured to emit anilluminating radiation; a lens unit configured to apply saidilluminating radiation in a direction which is substantially identicalto a direction in which said image capturing unit captures the image;and an irradiation moving unit configured to variably set an irradiationrange of said illuminating radiation to irradiate an area which issubstantially the same as said image capturing field angle of said imagecapturing unit.
 2. The monitoring camera according to claim 1, whereinsaid light source has a light guide configured to guide the illuminatingradiation from said light emitting diode to said lens.
 3. The monitoringcamera according to claim 1, wherein said light emitting diode includesan infrared emitting diode configured to emit an infrared radiation. 4.The monitoring camera comprising: an image capturing unit configured tocapture an image of a subject therein through an optical system; a lightsource including a plurality of light emitting diodes configured to emitan illuminating radiation; and a controller configured to controlenergization patterns of said light emitting diodes in synchronism withan image capturing timing interval of said image capturing unit.
 5. Themonitoring camera according to claim 4, wherein said controller hasmeans configured to change energization patterns of said light emittingdiodes to follow the subject when said controller detects the subject asmoving.
 6. The monitoring camera according to claim 4, wherein saidcontroller sets a first interval and a second interval shorter than saidfirst interval as emission intervals of said light source; and saidcontroller has means configured to control said light source to applysaid illuminating radiation entirely to an image capturing range of saidimage capturing unit if no moving subject is detected in an imagecaptured by said image capturing unit, and controlling said light sourceto apply said illuminating radiation to a portion of the image capturingrange if a moving subject is detected in an image captured by said imagecapturing unit, said portion of the image capturing range including saidmoving subject.